A gasoline engine operates on the principle of internal combustion. A fuel/air mixture is pulled into a cylinder, the cylinder is then closed off and the piston is thrust upward to create compression. A spark is then introduced to ignite the mixture to create combustion necessary to thrust the piston downward in the engine block. There are a number of pistons inside an engine depending on the design, 4 to 12 cylinders usually. The pistons are connected to a crankshaft through a connecting rod. Pistons fire consecutively to rotate the crankshaft inside the engine block. 

The oil pump pushes oil through the oil filter and then supplies oil to vital engine parts including the crank and camshaft, cylinder walls and piston rings, valve train, cam lifters and the timing gears or chain. Motor oil is used to lubricate and cool internal engine parts. Oil is pumped up through the engine, then returns to the bottom of the engine and is gathered in the oil pan. Motor oil is used to lubricate and cool internal engine parts.

The cylinder head is connected to the top of the engine block and allows the air/fuel mixture and exhaust into and out of the cylinder block. The cylinder head has the duty of holding the air/fuel mixture charge inside the cylinder as it is combusted, forcing the piston downward. The cylinder head is connected to the engine block using head bolts and using a head gasket to seal both parts together.

Overhead Cam Cylinder Head

A camshaft is used to open and close intake and exhaust ports by using valve train components. These components will vary depending on the design of the engine. There are primarily two styles of valve systems: "overhead cam" which consists of a camshaft and follower/rocker arm, and the "in block" system which consist of a camshaft, lifter, push rod, rocker arm. Both styles utilize a valve spring to hold the valve closed.

Car Acceleration

Acceleration is the process of changing the rate of velocity or movement. This is the result of available power from the engine. Usually, the bigger the engine, the power it makes. However, a turbo charged or supercharged (forced induction) engine provides an exception to the rule. When air is forced into an engine using a turbo/supercharger it can produce more power and improved acceleration with a smaller engine. Whenever you hear someone mention horsepower the first thing that usually comes to mind are cars; fast cars with extreme torque, muscle cars with lots of power, and vehicles capable of extreme speed. But why is horsepower so important? James Watt, a famous 19th century engineer, created the term "horsepower" in 1782 as he improved the power of the steam engine. 

While watching horses haul coal out of a coal mine he came up with the idea of defining the power exerted by these animals, thus the term "horsepower" was born. He calculated that a normal horse attached to a mill that ground corn or cut wood walked in a circle that was 24 feet in diameter. He then calculated that the horse pulled with a force of 180 pounds. Watt noticed the horse could make 144 trips around this circle in an hour. That is 2.4 trips per minute. Using these numbers he calculated that the horse traveled about 180.96 foot per minute then rounded up and came up with 181 foot per minute.

He then multiplied the 181 foot per minute by 180 pounds of force the horse exerted and came up with the number 32,580 foot pounds per minute then rounded up again to the number 33,000 foot pounds per minute. This number is equal to one horsepower. Mr. Watt used his new term to rate the power of the steam engine. Since most people were unfamiliar with the steam engine he had to come up with a comparison measurement that the farmer of the day would understand. As with any measurement there are different variations and different methods of measuring horsepower or hp. The normal measurement of horsepower is called mechanical horsepower.

Engine Compression

In a vehicle there are hundreds of moving parts that get you from the point A to point B. The modern automobile is an intricate piece of machinery and a wonder of the technological processes. One of the main processes that produces a vehicle's power is called compression. Compression is the pressure of the air/fuel mixture that has been compressed in the cylinder of the engine by the piston. As the piston travels upward this mixture is compacted down into a smaller volume so it can be ignited by a spark plug. In a four stroke engine compression occurs on the upward stroke or the upward push of the piston through the cylinder bore before the spark plug ignites the mixture.

Checking Compression

To check compression you must first disable the ignition system to keep the engine from starting. Locate the ignition coil and disconnect it, or unplug the ignition module connector. To test if the ignition is disabled crank the engine over, the engine should not start. With the engine warm remove one of the spark plugs and insert the compression tester into the spark plug hole. Now turn the key of the engine for at least 5 to 10 seconds to get an accurate reading. Repeat this for each cylinder of the engine and record your results relating the reading to the individual cylinder. If the individual readings vary by more than 10% between cylinders you may have a problem.

Optional compression testing methods include an electric starter tester. This test measures the battery amperage draw to each cylinder while the engine is cranking. It will show you which cylinders have good compression and which have the least compression. In a gasoline engine a moderate compression ratio is needed, around 140 to 160 pounds per square inch. Each manufacturer produces specific compression ratios for their engines to closely control the power output and emissions. If high compression exists it can cause a problem known as pre ignition or detonation. A compression test can detect internal combustion malfunctions such as, bad valves, bad piston rings, or excessive carbon build up. These problems if left un-repaired can cause more extensive engine damage and even catastrophic failure.

Octane Rating

Why should you read the octane rating at the gas pump? The compression ratio of your engine determines the octane required for optimum performance. The octane rating of gasoline states the level fuel that can be compressed before it ignites. Under extreme conditions such as heavy acceleration fuel can ignite without the use of the spark plug resulting in a "ping" or "pinging" and under ultra heavy condition a knocking sound. When this condition is left un-treaded it could result in sever engine damage.

The compression ratio is the number that can be used to help predict the engine performance. It is calculated by taking the volume of the cylinder, when the piston is at the bottom of its stroke, and then dividing it by the volume when the piston is at the top of the stroke, the higher the compression ratio the more power your engine can produce, The extra power produced is coupled with added efficiency in turn help improve gas mileage. (Note: most vehicles automatically adjust for different octane levels.)